The metric determines the type of chamfering that is done. If
the metric is equal to ‘taxicab’ a structure is generated
using generate_binary_structure with a squared distance equal to
1. If the metric is equal to ‘chessboard’, a metric is
generated using generate_binary_structure with a squared distance
equal to the rank of the array. These choices correspond to the
common interpretations of the taxicab and the chessboard
distance metrics in two dimensions.

In addition to the distance transform, the feature transform can
be calculated. In this case the index of the closest background
element is returned along the first axis of the result.

The return_distances, and return_indices flags can be used to
indicate if the distance transform, the feature transform, or both
must be returned.

The distances and indices arguments can be used to give optional
output arrays that must be of the correct size and type (both int32).